diff --git a/src/xpra/server/auth/sys_auth_base.py b/src/xpra/server/auth/sys_auth_base.py
index 64066f0130..b5b351f315 100644
--- a/src/xpra/server/auth/sys_auth_base.py
+++ b/src/xpra/server/auth/sys_auth_base.py
@@ -145,6 +145,7 @@ def authenticate_check(self, challenge_response, client_salt=None):
             ret = self.check(password)
             log("authenticate_check(..)=%s", ret)
         except Exception as e:
+            log("check(..)", exc_info=True)
             log.error("Error: %s authentication check failed:", self)
             log.error(" %s", e)
             return False